This application claims the priority of a Japanese Patent Application Number P4-251628 filed in Japan, on Sep. 21, 1992, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates in general to a guiding apparatus for guiding a rolled slab in a continuous hot roughing mill train, and in particular to a guiding apparatus suitable for preventing lateral curving, or snaking, of the rolled slab produced in a roughing mill of a V-H tandem configuration comprising edger mills and horizontal mills.
2. Technical Background of the Invention
Hot strip roughing train in a continuous hot rolling operation generally comprises a plurality of V-H tandem mills including edger mills, to control the width dimension of a rolled slab, and horizontal rolls to control the thickness dimension of the rolled slab. The rolled slab moving from upstream to downstream in a rolling train is first rolled through the edging mill disposed on the upstream side, and then enters the horizontal mill positioned on the exit side, i.e. the downstream side, of the edging mill.
At the entrance to the edging mill (the upstream side), there are entry side guides provided to guide the rolled slab into the edging mill, but there are no side guides on the exit side of the horizontal mill.
The entry side guide of the edging mill waits for, or stands by, the arrival of the incoming rolled slab while setting the guide spacing at about 50-100 mm wider than the width of the rolled slab so as to accommodate the incoming rolled slab to eliminate possibilities of mechanical interference. When the rolled slab arrives within the side guides, it is centered in the edging mill and the rolled slab is rolled while being guided within the above mentioned spacing. This type of mill is termed a standby type.
An improved design of the entry side guides, based on hydraulic driven guides, was disclosed in a report (in Japanese) entitled, "Method of improving stability of strip rolling", in the 51st Meeting of the Iron and Steel Institute of Japan, Hot Strip Rolling Seminar 51-4 held on Nov. 16-17, 1989.
There is also a proposal to dispose a side guide facility between the edging mill and the horizontal mill as disclosed in a Japanese Patent Application, First Publication, S63 (1988)-101004. This guide is also a standby type.
One of the problems in the slab rolling technology is lateral curving of the rolled slab as it exits the mill. FIG. 12 illustrates the degree of lateral curving, or snaking which occurs during rough rolling in a continuous hot rolling operation. FIG. 12(a) shows the extent of snaking measured at the center line of a rolled slab produced in a roughing mill (the fourth roughing stand R4), and shows that the head end HE and the tail end TE are bent towards the drive side. Similarly, FIG. 12(b) shows the extent of snaking of a rolled slab produced in a downstream roughing mill (the fifth roughing stand R5), and shows that the head end HE is bent towards the drive side, and the tail end TE is bent towards the work side, resulting in the formation of a S-shaped rolled slab. It is seen that such snaking occurs primarily in about a 3-5 m distance in the head and tail ends of a rolled slab, and such so-called "hooked nose" curving adversely affects the slab rollability, and contributes to the generation of wrinkling in the finish rolling process.
Lateral curving, or snaking, is caused by such reasons as off-centering of the rolled slab, widthwise temperature gradient in the rolled slab, uneven rolling pressures, other such factors. In the conventional side guide designs for the standby type of side guides, it is necessary to set the guides at a wide separation distance between the rolled slab and the guides so as to accommodate the incoming rolled slab smoothly, and therefore, it is not possible to completely prevent the formation of lateral curving. Even if centering of the rolled slab is performed hydraulically at the entrance to the edging mill, it is difficult to prevent the instances of lateral curving in the slab in the subsequent roughing mills.
In particular, the problem of lateral curving at the head end of the rolled slab has been attributed to the absence of the side guiding facility at the exit side of the horizontal mill, and the problem at the tail end of the rolled slab has been attributed to insufficient control on the guiding process after the tail end has left the edging mill.